This invention relates to manhole cover supports for emplacing over and raising the effective grade of an existing manhole cover-receiving structure, and more particularly to such supports that are to be resistant to water infiltration around them and/or are for accommodating a group of manhole covers of a standard size and shape where the frames thereunder diverge somewhat as to the size of the otherwise geometrically similar covers that they can take.
For simplicity the term "existing manhole cover-receiving structure" is used here to refer to the existing, i.e., fixed in-place frame or other seating receptacle for a removable cover or grating that covers an access hole (i.e., hand hole, tool hole, manhole, catch basin or the like). The term "manhole cover" is used to refer to the removable cover or grating over the access hole. The resulting assembly of a receiving structure and a manhole cover ordinarily is intended to bear vehicular traffic. The term "manhole cover support" or simply "cover support" here means a structure that fits over the existing manhole cover receiving structure, raises its grade, and thereby accommodates a cover or grating at the new elevated grade. The access hole covered is a utility enclosure serving, e.g., an electric, gas, water, sewer or storm drainage system.
The preponderance of manholes are circular (in street plan), have circular covers and have existing cover-receiving structures such as frames that are circular with circular cover keepers (also sometimes called "collars"). Accordingly, much of this specification is directed to round manhole cover supports that have ring-like annular elements which are to interact with an existing round manhole cover-receiving structure. However, it should be understood that this invention can be utilized in connection with other shapes of cover support, eg. rectangular, square, triangular, hexagonal and so on, and further that the instant cover support which is to be fitted to the usual circular hole of a frame can be adapted to take a round cover or one other than round, e.g. hexagonal, and still further this cover support need not have an outer periphery at pavement level that is round--that periphery can be, for example, square or octagonal.
Ordinarily a cover support finds its use when a roadway such as a street or highway is resurfaced with an added layer of paving material, typically asphalt concrete or sheet asphalt, to establish a higher grade. A principal use for the instant cover support is expected to be in a municipality where a group of manhole installations of somewhat varying diameters are likely to be encountered in the resurfacing. Thus, adjoining or the same subdivisions, boroughs, wards or districts may have existing manhole cover frames for accommodating a group of covers that are nominally of several fairly close sizes, say 221/2 to 24 inches in diameter. When resurfacing in such an area, it may be decided to standardize on a single size 23-, 24- or 25-inch diameter cover for this group to reduce the inventory of covers, purchase them in larger lots, avoid potentially costly custom-built equipment or short manufacturing runs, and certainly to eliminate the digging out, raising and resetting of the existing frames or other cover-receiving structures simply to accommodate their original variously-sized manhole covers. It then can be especially advantageous to mount the inventive cover supports atop these existing manhole cover frames for the standardization purpose.
Heretofore the typical installation of new manhole cover supports has seemingly been circumscribed by and restricted to the reuse of the old cover. The possible benefits of standardizing on a new cover size (and possibly shape) in place of a group of geometrically similar covers that vary a little in size from one to another or from one subgroup to another, then designing a new cover support expressly for the new standardized covers appears to have gone unrecognized; it does not seem to have been addressed at all by the art.
Apart from the economies available from and the simplicity of such standardization practice, the instant cover support also has another great advantage over conventional manhole cover supports, whether adjustable in periphery or not, in that its basic design renders its usual installation on a manhole cover frame inherently quite resistant to the infiltration of surface water from around its outer walls. Part of this is because its peripheral flange part (i.e. the fixed diameter top ring in the case of the usual annular cover support), usually has no gaps and generally is quite flat whether the peripheral flange is made in one unitary piece or is assembled from a plurality of abutting parts, e.g. with bolts.
The lack of such gaps in some prior unexpandable manhole cover supports is itself a conventional feature. However, the bottom of the peripheral flange of the instant cover support is borne, quite unconventionally, upon the top surface (rim) of the cover keeper of the existing manhole cover-receiving structure, e.g. a manhole cover frame, and that top surface (rim) ordinarily also is without gaps. The continuous, uninterrupted surfaces of the flange bottom and the receiving structure top rim in substantially horizontal contact with each other usually makes for a good blockage of surface water infiltration into the installation from around the outside of the new cover support. This cannot be achieved consistently using a conventional unexpandable cover support that is supported at least mainly if not entirely by the cover seat (and possibly some rising inside surfaces thereabouts) of the existing cover-receiving structure, e.g. the frame. Unless such unexpandable conventional cover support luckily just happens to fit the seat region of such receiving structure like a cork in a bottle, water leakage around a substantially looser fit is quite likely. Furthermore, because normal dimensional tolerances for castings such as cast iron manhole cover frames can be as much as .+-.1/8 inch per foot, it is rare that a truly leak-resisting fit will result between such cover support and such frame. In contrast, the peripheral flange of the new support resting on the rim of the frame of the inventive cover support generally effects water blockage without having to make a snug fit into any recess, but rather simply by being disposed on the rim that surrounds it.
The resistance of the instant cover support to surface water infiltration around the outer periphery of the instant support can be improved when a deformable water seal is interposed between the top of the keeper of the receiving structure (the rim) and the bottom of said peripheral flange.
Prior art on manhole cover supports and manhole cover frames can be found in U.S. Pat. Nos. 4,281,944, 4,236,358, 4,203,686, 3,968,600, 3,773,428, 4,225,266, 4,302,129, 4,097,171, 4,302,126, 3,891,337 and 1,987,502. The first five of these are for inventions of the applicant.
Axle loads up to 18,182 kg. must be resisted by many of these cover supports as well as serious impact loads from vehicles and snow plows, a variety of temperature effects, steam leaks, spillage, etc., without permitting a hazardous dislocation of the cover support or its cover. Often it is desirable also to cushion the cover for resisting wear or reducing noise, and/or to seal the cover and its cover support against a substantial and possibly overloading infiltration of surface water, e.g., storm drainage that otherwise would enter a sanitary sewer system at various manhole locations.
The instant cover support can be made especially highly resistant to displacement and dislodgement in service. Thus, while it preferably incorporates structural or mechanical holddown (anchoring) means to the existing manhole cover-receiving structure, such hook-like extensions that are integral with it or easily attached, it also can be constructed to do a good job of holding in (being retained in the existing manhole cover-receiving structure, such as a frame, while in service) by friction alone.
Also, the support lends itself readily and simply to being sealed off against water infiltration and to cushioning the cover. Its unique structure fills a place in street maintenance that has heretofore been neglected.